Optical testing apparatus for liquids



June A24', 1.941. y2,247,008v

OPTICAL TESTING APPARATUS FOR LIQUIDS F. ASSMUS Filed sept. 21. 1957 rfb.

j Fig. 7 Jawa f'zedfle r155mm? Patented June omciu. nismo ron u ooms Fl'lellrlchm allllllol' Gernnny ls, Freiburg, reisgall. Germany. r. neuke a co.. ruime. marsa.

Anneau@ semiasi, mi. sei-isi No. 164,865 In Germany october 2. 1936 s can ici. :ss-14) This invention relates' to the optical determil nation of chemical and other values, and lhas particular reference to the determination of the hydrogen ion concentration value. the so-called pH value-of solutions and the like by optical comparison of the color of a solution or the like with a colored reference.

It is known that the color of certain coloring agents varies with the pH value of their solutions. and this value is a measure of their' acid or basic value.

Conversely, the color variation can be utilized.

for the optical determination of the pH value by means of a reference and a calibrated color scale.

Apparatus for this purpose havealready beendevised but are comparatively complicated and expensive and their operation is not perfect.

It is an object of the invention to provide an apparatus of the kind described which is veryA simple and consequently cheap while at the same time it is easy toienipmate and reliable.

To'this end the apparatus is equipped with a frame, preferably erected on a suitable base, and having a .rectangular opening, On this frame is mounted to slide a box-shaped support for the liquid under test which is normally placed in a cuvette inserted in the support. The support has a hole for looking through the liquid and two more holes for respectively viewing a ref lerence strip and a scale. 'Ihe reference 'strip and the scale are placedin a detachable holder and means are provided for securing the holder to. the frame.

. The apparatus comprises a plurality of selicontained and exchangeable units and requires but a fewmanipulations for assembling and dis'- assembling it. 'I'he reference strip and the scalev can be readily exchanged for others which, for instance, may have been purchased later by the operator.

The measuring elements, i. e. the color scale, the reference strip and the cuvette, are combined and adjusted in a novel manner.

Delicate parts of the apparatus are so arranged that they will not be damaged by frequent operation. l

A further object of the invention is to provide means-for'obtaining transition colors.

To this end the reference strip is made ofl a pair oi superimposed colored wedges the densities of which vary in opposite directions.

The objects of the invention are attained by connecting the several parts representing the values to be compared in a common frame so t'V at they are adjustable with respect to each o er. and readily exchangeable. In the accompanying drawing. an apparatus embodying the invention is illustrated by way of example:

Fig. 1 is a front elevation.

Fig. 2 is a side elevatio Iviewedfrcm the left in Fig. 1. and

Fig. 3 is a rear elevation of the apparatus with the holder for the scale and reference removed..

lIl'igs. 4 and 5 are sections on lines IV-IV and V-V in Fig. 1 respectively.

. The apparatus comprises a Pig. 6 shows m front view -the holder with e.

l scale and reference strip.-

Rig. 7 is an end elevation of the holder, viewed from the rient in Fig. c.

Iii'g 8 is a section on line VIII--VIII- of Fig. 6,

Fig. 9 is colored wedges referred to.

on the base, here shown with a rectangular opening, a detachable holder I4 for a plate of transparent glass with color scale and reference strip, and a slide 6a4 which isguided by rebates I in lthe front side of frame 2 and to which is secured a box shaped support 5. A rib 6b projecting fnwardly from thefront wall of the support 5 sub-V dlvides it into two compartments 8 and 1. 8 .is

- a peep hole at the left in said support for view inganindex 2l, asV will be described, 9 is a peep hole for looking through the liquid under test in a cuvette 2l .inserted in compartment 6, Fig. 4, and il is a peep hole for viewing the colored reference strip. Referring now to Fig. 3 showing the apparatus from the rear the holder Il having been removed, 2l is a blade spring 'on the slide la and the free end of* the blade spring bears against the corresponding inner face of frame 2 to hold the slide in position by friction, and 2 is a clip in which a color screen, not shown, can be inserted if desired. I I are rebates at the rear of the frame 2 for the reception of a holder Il which, as shown in Fig. 8. has channel cross-section, a pair of inwardly projecting edges at its ends defining a rectangular opening. The holder I4 is placed in the rebates `Il of the frame and held by a laminated spring il inserted in'a space i2 between the rear side of frame 2 and a short vertical abutment Ia.

A front plate l inserted in the holderl Il behind the inwardly projecting edges mentioned ya part vertical sect-ion showing the base I, a frame! are inserted in the frame Il behind the front plate 3. 'I'hese plates are of glass ory any other suitable material, the front plate I8 being transparent and the rear plate I9 being translucent,

for instance of ground glass. Between the plates I 8 and I9 a colored reference strip 20 and a scale 2I are located. -The scale 2l has numerals 22 preferably produced by photographic blackening of a sensitized layer and here showing pH values, and a transpartent area 23 at the side of the numerals which is in line with hole 9.

Ihe reference strip 20 and the scale 2| consist of layers of gelatine attached to the back of the transparent glass plate I 8.

To obtain in the reference strip 20 a gradual change of color corresponding to the change which occurs in liquids whose pH value is to be determined, the reference strip 20 preferably is composed of two superimposed color wedges 28 and 29 enclosed between the plates I8 and I9, Fig. 9. lEach wedge is of diierent color, for instance, the color of the front wedge 28 is purple,

and that of the rear wedge 2S is yellow. The

densities` of the wedges vary in opposite directions, that is, the density of the front wedge 28 decreases from its upper to its lower end, and the density of the rear wedge 29 decreases from its lower to its upper end. By these means a uniformv and gradual change from purple to yellow is obtained.

The operation of the apparatus is 'as follows:

The cuvette 24 is filled with a solution whose pH value is to be determined and to the solution a coloring agent for producing the necessary change of color is added. It has been supposed.`

that the substance under test is a solution oi.' brome kresol purple whose pH value is 6.8 to 5.2 as shown on the scale 2l. The box-shaped support 5 is raised and lowered until the same color appears in the peep holes 8 and II). 'I'he corresponding pH value, 6.2 in the present instance, is indicated in the peep hole 8 by the index 25.

If desired, a cuvette 24a is filled with a color compensation liquid and placed inthe compartment l of the box-shaped support 5.

The apparatus may be made of any suitable material and preferably its parts are produced by molding under pressure a suitable composition of articial resin. This reduces'the cost of manuof the apparatus is not limited to the determination of pH values, as described by way of example, but can be used in all cases where it is desired to compare colors.

The simplicity of the apparatus will appear from the foregoing description.' It comprises self-contained and exchangeable units and the ease of its operation and manipulation due to the several improvements en'ected is obvious. Providing the holder Il for the plate I8 with the scale' and the color reference has the advantage that the plate is readilyl exchangeable for any plate which the operator may purchase.

I claim:

1. An apparatus for testing the pH values o1' liquids, comprising in combination a base, an open rectangular frame upright in said base, guides on said frame, a box-shaped support on the iront side of said frame vertically slidable in said guides and having three peep holes arranged side by side in the same horizontal plane, an index in the left peep hole, a short partition separating said support into twochambers; a plate of transparent glass and a. plate of translucent glass removably tted in the rear end of said frame, a reference strip of non-uniform color, a measuring scale gauged to the pH values o f said reference strip both the strip and the scale attached to the rear sidegoi! said plate of transparent glass, a transparent vessel for the liquid to be tested removably inserted in the left hand compartment of said support said vessel and support adapted to be moved into horizontal alignment with the color value on said reference strip corresponding to the color of the liquid in said vessel, the pH value oi the liquid of this color value being readable on said measuring scale through the left peep hole.

2. In an apparatuses specified in claim 1, a second vessel lled with compensation liquid removably inserted in the right hand compartment of the box-shaped support.

3. An apparatus as speciiied in claim 1, in which the reference strip behind the plate of transparent glass is composed of two superposed differently colored wedges the density of the front wedge decreasing from the upper to the lower end and the density of the rear wedge decreasing from the lower to the upper end.

rnmnmcn AssMUs. 

